In recent years, attention is focused on aromatic cyclic compounds because of their potential as high-function or functional material owing to characteristics originating in their cyclic structures, i.e., their unique features based on their structures to serve as compounds with clathration capability or as useful monomers that undergo ring opening polymerization to synthesize a high molecular weight, straight-chain polymer. The cyclic polyarylene sulfide (hereinafter, polyarylene sulfide will be occasionally abbreviated as PAS) falls in the category of aromatic cyclic compounds, and deserves such attention as described above.
A process proposed for production of a cyclic polyarylene sulfide is to perform oxidation polymerization of, for instance, a diaryl disulfide compound under ultradilute conditions (for instance, see Patent document 1). It is expected that this process produces a cyclic polyarylene sulfide highly selectively, without significant formation of linear polyarylene sulfides, making it possible to obtain a cyclic polyarylene sulfide with a high yield. However, this process essentially requires reaction under ultradilute conditions, and can produce a very small amount of cyclic polyarylene sulfide per unit volume of the reaction container used, and therefore, the process is problematic in view of efficient production of a cyclic polyarylene sulfide. Said process, furthermore, uses oxidation polymerization and essentially requires mild conditions around room temperature. Thus, the reaction has to be performed for a lengthy period of time, say, several tens of hours, and is inferior in terms of productivity. Polyarylene sulfides resulting as by-products from said process are low molecular weight ones containing disulfide bonds originating in the diaryl disulfide fed as starting material. They have a molecular weight close to that of the target cyclic polyarylene sulfide, making it difficult to separate the cyclic polyarylene sulfide from by-product polyarylene sulfides. Thus, it is very difficult to produce a high-purity cyclic polyarylene sulfide efficiently. For said process, furthermore, an expensive oxidation agent such as dichlorodicyanobenzoquinone is as necessary as the feed diaryl disulfide to advance the oxidation polymerization, preventing the production of a cyclic polyarylene sulfide at low cost. Another process that has been proposed uses oxygen as oxidation agent while carrying out oxidation polymerization under the existence of a metal catalyst. Though the oxidation agent for this process is available at low price, the control of the reaction is difficult and a wide variety of by-product oligomers will be formed in large amounts. There are other problems such as the need of a length period of time for the reaction. In any case, it is impossible to produce a high-purity cyclic polyarylene sulfide efficiently at low cost.
Another cyclic polyarylene sulfide production process that has been disclosed uses the copper salt of 4-bromothiophenol which is heated in quinoline under ultradilute conditions. As in the case of Patent document 1, this process also essentially requires ultradilute conditions, and the reaction requires a lengthy period of time. The productivity of the process, however, is very low. It is also difficult to separate the by-product copper bromide from the target cyclic polyarylene sulfide, and the cyclic polyarylene sulfide has a low purity (for instance, see Patent document 2).
To produce a cyclic polyarylene sulfide at a high yield, a process that has been disclosed allows a dihalogen aromatic compound, such as 1,4-bis-(4′-bromophenyl thio)benzene, to come in contact with a sodium sulfide in N-methylpyrrolidone at a reflux temperature(for instance, see Nonpatent document 1). This process uses 1.25 liters or more of an organic polar solvent for 1 mole of a sulfur component in the reaction mixture, suggesting that a cyclic polyarylene sulfide will be produced. However, since linear polyarylene sulfide is not used as feed material, it is necessary to feed a dihalogen aromatic compound in large amounts. A very special type of dihalogen aromatic compound is needed, furthermore, and the industrial practicability of the process is very low, requiring efforts to improve it.
To produce a cyclic polyarylene sulfide from common feed materials, a process has been disclosed which allows p-dichlorobenzene, i.e., a dihalogenated aromatic compound, and sodium sulfide, i.e., an alkali metal sulfide, to react in N-methyl pyrrolidone, i.e., an organic polar solvent, followed by removing the solvent while heating under reduced pressure and washing the product. The resulting polyphenylene sulfide is subjected to extraction with methylene chloride and the target substance is recovered from the saturated solution portion of the extract obtained (for instance, see Patent document 3). The problem with this process is that the major portion of the product is accounted for by high molecular weight polyphenylene sulfide, and the cyclic polyarylene sulfide can be obtained in very small amounts (at a yield of less than 1%).
Also disclosed are polyarylene sulfide production processes in which an aromatic compound or thiophene containing at least one nuclear-substituted halogen atom is reacted with an alkali metal monosulfide in a polar organic solvent at a raised temperature (for instance, see Patent document 4, Patent document 5 and Patent document 6). Unlike the purpose of the invention, these processes aims to provide polyarylene sulfides and the documents contain nothing concerning the production of cyclic polyarylene sulfides. These processes, which aim to produce polyarylene sulfides with high molecular weights, use smaller amounts of organic polar solvents relative to the amounts of sulfidizing agents and the documents not only disclose nothing about reactions that involve 1.25 liters or more of an organic polar solvent per mole of the sulfur atoms in the sulfidizing agent used, but also describe clearly that a useful product cannot be obtained if more than one liter of a organic polar solvent is used per mole of the sulfur atoms in the sulfidizing agent. Furthermore, they describe nothing about the use of a linear polyarylene sulfide as feed material.
To produce an arylene sulfide based polymer by using a linear polyarylene sulfide as feed material, a process has been disclosed in which a polyarylene sulfide is reacted with an alkali metal sulfide to cause depolymerization and the resulting prepolymer with an alkali thiolate group at least at one end is reacted with a dihalogenated aromatic compound to cause polymerization (for instance, see Patent document 7). This process, which relates to the modification of a polyarylene sulfide, not only is designed for a purpose different from that of the present invention, but also the document describes nothing about the production of a cyclic polyarylene sulfide. Furthermore, since this process aims to produce a high molecular weight polyarylene sulfide, the document only discloses a reaction that involves about 1 kg or less of an organic polar solvent per mole of the sulfur components in the reaction mixture and describes nothing about a reaction that involves 1.25 liters or more of an organic polar solvent per mole of the sulfur component in the reaction mixture. This process essentially requires a two-step reaction in which a polyarylene sulfide is reacted with an alkali metal sulfide to prepare a prepolymer with an alkali thiolate group at at least one end, followed by polymerizing this prepolymer and a dihalogenated aromatic compound. As compared with embodiments of the invention in which a linear polyarylene sulfide, a sulfidizing agent and a dihalogenated aromatic compound are reacted together, the above-mentioned has many problems including the necessity of accurate reaction control and difficult operations.
There are other disclosed processes in which a polyarylene sulfide used as feed material is reacted with an alkali metal sulfide. In one of them, a thiolate group is introduced to an end of a polyphenylene sulfide to produce a highly reactive polyphenylene sulfide (for instance, see Patent document 8) while in others, a polyarylene sulfide is reacted with an alkali metal sulfide to synthesize a prepolymer with an alkali thiolate group at least one end, followed by reaction with various dihalogenated aromatic compounds to produce polyarylene sulfide based copolymers (for instance, see Patent documents 9 to 12). These processes, however, have purposes different from that of embodiments of the present invention, and the documents not only describes nothing about cyclic polyarylene sulfides, i.e., the target of embodiments of the invention, but also describes nothing about a reaction that involves 1.25 liters or more of an organic polar solvent per mole of the sulfur component in the reaction mixture.    [Patent document 1] Japanese Patent Registration No. 3200027 (Claims)    [Patent document 2] U.S. Pat. No. 5,869,599 (p. 14)    [Patent document 3] Japanese Unexamined Patent Publication (Kokai) No. Hei 05-163349 (p. 7)    [Patent document 4] Japanese Examined Patent Publication (Kokoku) No. Sho 45-3368 (p. 6 to 8)    [Patent document 5] Japanese Examined Patent Publication (Kokoku) No. Sho 52-12240 (p. 10 to 20)    [Patent document 6] Japanese Examined Patent Publication (Kokoku) No. Sho 63-3375 (p. 6-9)    [Patent document 7] Japanese Unexamined Patent Publication (Kokai) No. Hei 04-7334 (Claims)    [Patent document 8] Japanese Unexamined Patent Publication (Kokai) No. Hei 02-140233 (Claims)    [Patent document 9] Japanese Unexamined Patent Publication (Kokai) No. Hei 04-213329 (Claims)    [Patent document 10] Japanese Unexamined Patent Publication (Kokai) No. Hei 04-311725 (Claims)    [Patent document 11] Japanese Unexamined Patent Publication (Kokai) No. Hei 05-043689 (Claims)    [Patent document 12] Japanese Unexamined Patent Publication (Kokai) No. Hei 05-98007 (Claims)    [Nonpatent document 1] Bull. Acad. Sci., vol. 39, p. 763-766, 1990